DEVELOPMENT OF ADULT-TYPE INHIBITORY GLYCINE RECEPTORS IN THE CENTRALAUDITORY-SYSTEM OF RATS

Inhibitory synaptic activity is crucial for many aspects of acoustic i nformation processing and mainly mediated by glycine and gamma-aminobu tyric acid, the two principal inhibitory neurotransmitters in the audi tory system. Glycine exerts its inhibitory action via binding to posts ynaptic receptors existing in various isoforms. Here we have investiga ted the spatiotemporal distribution of adult-type, strychnine-sensitiv e glycine receptors (GlyRs) in the rat auditory system by using a spec ific antibody against the ligand-binding alpha 1 GlyR subunit. In adul ts, alpha 1 GlyRs were found at all relay stations of the auditory pat hway except for the medial geniculate body and the auditory cortex. In most brainstem nuclei, labeling was characterized by dense clusters o f heavily immunoreactive puncta outlining the somata and proximal dend rites, indicative of a powerful glycinergic inhibition. No alpha 1 imm unoreactivity was seen in the auditory system of fetal rats, consisten t with results obtained by others in the spinal cord. At birth, labeli ng was weak and restricted to defined nuclei of the cochlear nuclear c omplex and the superior olivary complex. By postnatal day 8, labeling was seen in all brainstem nuclei. At the first appearance of immunorea ctivity, alpha 1 GlyRs were diffusely distributed on the neuronal surf ace, yet they became clustered with age, finally densely incrusting th e somata and proximal dendrites between the 3rd and 4th postnatal week , when the mature pattern of immunoreactivity was established. We neve r observed an overexpression of alpha 1 GlyRs or a transient appearanc e in areas that are devoid of the receptor in adults. The late formati on of glycinergic synapses harboring the adult-type GlyRs in the audit ory system, at a time when internuclear connections have already forme d, indicates that alpha 1 GlyRs do not participate in early synaptogen esis. (C) 1997 Wiley-Liss, Inc.